1. Field of the Invention
The present invention relates to tools and methods for welding, coating, repairing, or otherwise modifying the surface of a metal substrate. More specifically, and as shown in FIGS. 1A-B, the present invention relates to self-reacting friction stir welding tools which have an internal channel that allows filler materials to be added to the weld joint or otherwise friction stir processed area.
2. Description of Related Art
Friction stir welding (FSW) is a solid-state welding process in which a rotating non-consumable tool consisting of a cylindrical shoulder with a pin protruding from the bottom translates along the weld axis, and as the tool rotates and translates the base metal is heated and plastically deformed mixing metal from the two plates together. Exemplary publications relating to friction stir welding include European Patent Nos. 0 615 480 B1, and 0 752 926 B1, the disclosures of which are incorporated by reference herein in their entireties.
In a typical FSW Implementation, a backing anvil is located under/behind the workpieces being joined to support the workpieces and react to the load imparted by the tool. To maximize strength of the joint between workpiece sections, the welded portion should extend the entire thickness of the workpiece and the plasticized region should extend between upper and lower surfaces of the workpiece.
Due to variations in thickness of workpieces, the depth of the pin penetration into the joint can vary. If pin depth does not extend sufficiently into the joint, the plasticized region may not extend the entire thickness of the workpiece, which may lead to stress notches in the joint. Likewise, for variations to smaller thicknesses, the pin can extend too close to the backplate so that the workpiece becomes joined to the backplate during welding.
Self-reacting friction stir welding (SRFSW) tools, such as U.S. Pat. No. 6,199,745, the disclosure of which is incorporated by reference herein in its entirety, eliminate the need for a backing anvil and as such are an ideal tool choice for FSW where backside access is restricted such as in ship yard assembly of prefabricated panels. This patent describes a welding head including upper and lower probe members and probe pin, where the upper and lower probe members are independently actuatable and biased to follow the profile of a workpiece and supply a balance load to opposed surfaces of a workpiece during welding operation. Shown in FIG. 2 is an example of a typical self-reacting type tool.
A major drawback of SRFSW type tools are the added complexity of requiring movable shoulders to increase or decrease the spacing between the shoulders depending on the thickness of the plate being welded. Additionally, variation in the thicknesses of plates being welded can lead to under and/or over penetration of the shoulder thus thinning the weld on the thick side and loss of shoulder contact on the thin side.
To address some of these manufacturing difficulties, the present inventors have proposed a novel self-reacting stirring tool with no relative movement between shoulders and in operable communication with a system for continuously feeding filler material to the tool.